The present invention pertains to the treatment of metal surfaces in order to improve the corrosion resistance thereof. More specifically, the invention provides a novel and improved emulsified oil composition, usually referred to as a "phosphating oil", and method of treating phosphated metal surfaces therewith.
In the field of metal surface treatment, it is of considerable importance to provide metal surfaces with the maximum degree of resistance against corrosion. Otherwise, corrosion can readily attack either ferrous or non-ferrous metals, which are routinely exposed to corrosive agents and environments. For example, corrosion can result from the presence of water and oxygen causing the formation of rust on ferrous metal surfaces, or from oxidation or formation of metallic residues on non-ferrous metal surfaces.
One known way to inhibit corrosion has been to subject metallic surfaces to a "phosphating" treatment. For purposes of the present invention, the terms "phosphating" or "phosphated" refer to treatment by which a metal surface is rendered relatively inactive to attack by corrosive agents by formation or deposition thereupon of adherent crystalline deposits of phosphate salts. Typically, a phosphating treatment involves immersion of the metal surface in a hot aqueous solution containing phosphoric acid and/or phosphate salts, as well as one or more other organic salts, such as zinc nitrate, calcium nitrate, copper sulphate, etc. As a consequence, the solution acts chemically on the metallic surface, so that the desired crystalline phosphate deposit forms and adheres thereupon. This provides an initial passivation of the metal surface against attack by corrosive agents or environments and is a technique which is well known and used commercially in the art.
It is also known that the degree of corrosion resistance provided by phosphated metal surfaces can be enhanced by application of an oil composition which adheres to the phosphated surface and further prevents penetration of water, oxygen or other corrosive agents. Typically such an oil composition, commonly referred to as a "phosphating oil", comprises an aqueous emulsion of an oil composition, which may contain stabilizers, emulsifying agents and extenders and other additives.
However, even phosphated metal surfaces to which a phosphating oil has been applied provide insufficient corrosion resistance for certain environments and applications. In accordance with the present invention, a novel and improved phosphating oil composition has been developed which can provide in excess of a 100% increase in the degree of corrosion resistance of the phosphated metallic surface to which it is applied. Thus, the present invention constitutes a substantial and beneficial improvement over prior art techniques, compositions and methods.
Accordingly, the primary object of this invention is to provide an improved phosphating oil composition which yields substantially improved and superior corrosion resistance in comparison with conventional phosphating oil compositions.
It is a further object of the invention to provide a novel bath and method for treating phosphated metal surfaces, so as to impart superior corrosion resistance properties thereto.
It is yet a further object of the invention to provide additives for conventional phosphating oil compositions which improve the corrosion resistance properties thereof in applications over phosphated metal surfaces.